Regional differences in the age and growth of red snapper (Lutjanus campechanus) in the U.S. Gulf of Mexico

Abstract

Abstract-In the U.S. Gulf of Mexico (GOM), red snapper (Lutjanus campechanus) are managed as a unit stock, although the stock is assessed as subunits east and west of the Mississippi River. Differences were examined between management subunits by comparison of the size and age structure and growth rates of red snapper among recreational catches from 6 regions of the GOM: South Texas, North Texas, Louisiana, Alabama, Northwest Florida, and Central Florida. In all of these regions, red snapper sampled in 2009 and 2010 were small and predominantly from age classes that represented the strong recruitment for the year classes of 2004-06. As such, our data indicate a highly truncated age structure with few fish older than 6 years. Demographic differences in size, age, and growth parameters were found. Small (≤550 mm in total length), fast-growing individuals dominated the catches in South Texas and the regions of Florida, whereas larger, slower-growing fish represented the majority of catches in Alabama and Louisiana. The potential mechanisms affecting observed demographic variation include environmental differences, fishing pressure, habitat preference, and management regimes; however, no definitive conclusion about cause and effect can be made. The combination of demographic differences between regions and consistent occurrence of the strong year classes GOM-wide supports recent conclusions that red snapper form a metapopulation of semi-isolated assemblages in the GOM.

James's rule and causes and consequences of a latitudinal cline in the demography of John's Snapper (Lutjanus johnii) in coastal waters of Australia

“…For example, Allman and Goetz (2009) and Burton (2001) reported that mean size at age in Gray Snapper (Lutjanus griseus) in Florida in-creased with distance from the equator, but they invoked major regional differences in exploitation rate as an explanation. At a smaller latitudinal scale, Saari (2011) 2 were concerned that sample sizes were too small for any inferences to be made from such observations. There is no doubt that heavy fi shing can affect body sizes of fi shes across latitudes.…”

Temporal and spatial comparisons of the reproductive biology of northern Gulf of Mexico (USA) red snapper (Lutjanus campechanus) collected a decade apart

“…While the two subpopulations in the northern Gulf are not genetically distinct [9], demographic differences exist in sizes at age and maturation rates [10–12]. It has been suggested that these demographic differences may be adaptive responses to factors including differing fishing mortality rates, habitat complexity including numbers of deployed artificial reefs versus natural reef outcroppings, and regional population sizes [10–12]. …”

“…Significant declines in stock size [4], and the removal of older individuals [13, 14] appears to have resulted in a phenotypic stress responses, including early maturation [11], faster growth [10, 12, 14] and smaller sizes-at-age [12, 14]. This is problematic because increased reliance on younger, smaller fish limits reproductive potential and resilience, and slows recovery from overfishing [17].…”

“…A rebuilding target of 26% SPR for the U.S. Gulf, (i.e., 26% spawning potential ratio for both areas combined) has been in place for more than 20 years; this benchmark rebuilding target must be reached by 2032 in accordance with regulatory Amendment 22 to the Reef Fish Fishery Management Plan and the Sustainable Fisheries Act [5, 13]. Although overfishing is no longer occurring, the stock remains overfished with a highly truncated age structure [5, 12, 16]. …”

Application of Otolith Chemical Signatures to Estimate Population Connectivity of Red Snapper in the Western Gulf of Mexico

“…This was attributed to signs of juvenescence in the SWG population as it rebuilds from overfishing, whereas the NWG population may have moderate to low fecundity and later maturation due to its higher population size. Therefore, it is possible for the SWG population to be locally derived during strong year-classes (e.g., 2005 cohort;Cowan 2011;SEDAR 2013;Saari 2014) and to receive recruitment from other regions when year-classes are not as strong (e.g., 2007 cohort). Thus, in combination with past research on Red Snapper, the observed classification proportions in this study indicate the NWG's importance as a source of recruits to Red Snapper populations in the western U.S. Gulf.…”